Grainyhead-like 2 downstream targets act to suppress EMT during neural tube closure

Abstract

The transcription factor grainyhead-like 2 (GRHL2) is expressed in non-neural ectoderm (NNE) and Grhl2 loss results in fully penetrant cranial neural tube defects (NTDs) in mice. GRHL2 activates expression of several epithelial genes; however, additional molecular targets and functional processes regulated by GRHL2 in the NNE remain to be determined, as well as the underlying cause of the NTDs in Grhl2 mutants. Here, we find that Grhl2 loss results in abnormal mesenchymal phenotypes in the NNE, including aberrant vimentin expression and increased cellular dynamics that affects the NNE and neural crest cells. The resulting loss of NNE integrity contributes to an inability of the cranial neural folds to move toward the midline and results in NTD. Further, we identified Esrp1, Sostdc1, Fermt1, Tmprss2 and Lamc2 as novel NNE-expressed genes that are downregulated in Grhl2 mutants. Our in vitro assays show that they act as suppressors of the epithelial-to-mesenchymal transition (EMT). Thus, GRHL2 promotes the epithelial nature of the NNE during the dynamic events of neural tube formation by both activating key epithelial genes and actively suppressing EMT through novel downstream EMT suppressors.

Inactivation of Zeb1 in GRHL2-deficient mouse embryos rescues mid-gestation viability and secondary palate closure

“…We have shown that the epithelial abnormalities observed in Grhl2 −/− non-neural ectoderm at E8.5 (Ray and Niswander, 2016) also occur in PA1 epithelium at E10.5. This implies that other aspects of the Grhl2 mutant mouse phenotype, such as thoracogastroschisis (Pyrgaki et al, 2011), are also a consequence of epithelial dysfunction.…”

“…As GRHL2 is required to maintain the epithelial integrity of nonneural ectoderm at E8.5 (Ray and Niswander, 2016), we determined whether absence of this transcription factor perturbs E-cadherin and vimentin expression at E10.5. The first pharyngeal arch (PA1) comprises the MXPs, which form the palate, and the MDPs, which form the lower jaw.…”

“…Embryos carrying N-ethyl-N-nitrosourea (ENU)-induced mutations in Grhl2 can survive until advanced stages of development, at which point they display a cleft upper jaw (Menke et al, 2015;Pyrgaki et al, 2011). The non-neural ectoderm adjacent to the neural plate displays mesenchymal characteristics in Grhl2 mutant embryos, including aberrant vimentin expression and increased cell motility (Ray and Niswander, 2016). The resulting lack of epithelial integrity prevents apposition of the neural folds, resulting in failed neural tube closure.…”

A novel mechanism of gland formation in zebrafish involving transdifferentiation of renal epithelial cells and live cell extrusion

“…Here, the neural plate undergoes apical constriction and invaginates before pinching off as the neural tube while the surrounding non-neural ectoderm fuses together (Nikolopoulou, Galea, Rolo, Greene, & Copp, 2017). The exact molecular mechanism for how barrier function is maintained during neural tube closure is not fully understood but epithelial-tomesenchymal (EMT) transitions appear suppressed (Ray & Niswander, 2016).…”

Novel role for Grainy head in the regulation of cytoskeletal and junctional dynamics during epithelial repair

“…In vertebrates, TFs of the Grhl family, homologs of Grh, have been shown to be important in preventing EMT (Cieply et al, 2013;Farris et al, 2016;Ray and Niswander, 2016) and their misregulation has been observed in different types of tumors (Cieply et al, 2012;Mlacki et al, 2015). It is still not well understood how Grhl TFs regulate these events, but a link to AJs is likely.…”